Update targetHAL_Time.cpp (#548)
Update targetHAL_Time.cpp (#548)

Fixes nanoframework/Home#257.

Now, with a time set internally to 12/17/2017 08:00:00, 
`Console.WriteLine("utcNow : " + DateTime.UtcNow.ToString());`
is returning 
`utcNow : 12/17/2017 08:00:39`  (The 39 seconds are due to the manual startup time of the debug session after the board's reset)
Eclo/nf-interpreter,nanoframework/nf-interpreter,nanoframework/nf-interpreter,Eclo/nf-interpreter,Eclo/nf-interpreter,nanoframework/nf-interpreter,nanoframework/nf-interpreter,Eclo/nf-interpreter